Download 07110059, 07110100 & 07110067

Designing and Empirical Realization of Horn antennas and
Waveguides in a 60 GHz Wi reless System
A Thesis
Submitted to the Department of Electrical and Electronic Engineering
\
of
BRAC University
By
Sk. Laila Ayesha-071 10059
Synthia Aman-0711 01 00
Sumaiya Akhter-071 10067
In Partial Fulfillment of the
Requirements for the Degree
of
Bachelor of Science in Electronics and Communication Engineering
Apri l 2010
BRAC University, Dhaka , Bangladesh
DECLARATION
We hereby declare that this thesis is based on the res ults established by us.
Materials of work found by other resea rchers are mentioned in the reference.
This thesis, neither in whole nor in part, has been previously submitted by any
degree.
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5l.<. Lo.; 10..
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sa~()...
Signature of Supervisor
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fh.ro.1l-
Signature of Students
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ACKNOWLEDGMENTS
Special
thanks
to
honorable
supervisor
Dr.
Ahmed
Kama l,
Professor,
Department of Electrical and Electronic Engineering, Brac University, Dhaka for
accepting the difficult task of overseeing this work to completion. The authors
would specially express their most sincere gratitude to Mr. Apurba Saha,
Lecturer, BRAC University for taking time out of thei r busy schedules to consider
this work.
2
iii
ABSTRACT
Wireless Communications in the unlicensed 60G Hz band are becoming
increasingly com mercially attractive and popular. This paper focuses on to
design and empirical realization of building a pyramidal horn antenna and
waveguides for such a high frequency system. Antenna is an integ ral part of
receiving and transmitting information at a much faster rate at this high
freq uency.
Therefore, a pioneer step is taken in order to design a 60GHz antenna with
waveguide stru ctures. The antenna system will be tested for data tran smission
and polarization diversity can also be verified for ve rtical , horizontal, slant, left
circu lar, right circular and elliptical polarization in the futu re development of the
thesis work.
3
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iv
Table of Contents
TITLE ....... ... ......... ... ... ... ... ... .. .. ..... ..... .... ... .... ...... ... ... ...... ....... .......... .............. . i
ACKNOWLEDGEMENTS ..... ... ..... ... ..... ...... .. .... .. .... ....... .... .... .... ..... .... .. .. .... .. ... ii
ABSTRACT. .... .. .... ........ .......... ... ...... .... .... .. ..... .. .. ..... .... .. ... .. .. ................. .. ...... .iii
TABLE OF CONTENTS .. .. ... .......... .... .. .............. ...... .......... ...... ............ ........... . iv
List of Figures ... ...... .... ... ..... ... .... ....... ......... ......... .. ... .......... ...... .... ....... .. ............. v
CHAPTER I
Introduction
1.1 Introduction to Communication System
8
1.2 60 GHz Frequency System
9
1.2.1 Unlicensed bandwidth
1.2.2 Reasons of using 60 GHz frequency
9
10
1.3 Electromagnetic energy
14
1.3.1 Electric Charge
1.3.3.Magnetism
14
14
14
1.3.4 Electromagnetic Wave Energy
14
1.3. 5 Electromagnetic Spectrum Energ y
15
1.3.6Electromagnetic Radiation Energy
15
1.3.7Electromagnetic Field Energy
15
1.3.2 Electric Current
4
1.3.8 Electromagnetic Energy Facts
1.4 Radio Frequency (RF) commun ication
1.4.1 Microwave frequency
15
17
18
1.5 Transferri ng of electromagnetic waves
19
1.5.1 The two-wire transmission line
19
1.5.2Coaxial lines
20
1.5.3 Waveguides
21
1.5.3.1Waveguide Advantages
21
1.5.3.2Waveguide Disadvantages
22
1.6 Wavegu ide design
1.6.1Dimensions
1.7 Horn antenna
23
23
28
1.7.1 Why Horn Antenna
29
1.7.2 Classification of horn antenna
30
1.8 Dipole
31
1.9 Oscillator
32
1.9.1 Crystal Oscillator
34
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5
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CHAPTER 2
Design and Calculations
2.l Waveguide
36
2.2 Hom antenna
39
2.2.1 60 GHz hom antenna calculations
41
2.2.2 10GHz hom antenna calculations
44
47
2.3 Dipole design
CHAPTER 3
Conclusion and Further work
3.1 Conclusion
51
3.2 Future Works
51
References
52
6
LIST OF FIGURES
Figure
Page
Figure 1.1 Unlicensed spectrum
9
Figure 1.2 Attenuation versus frequency
10
Figure 1.3 Radiations Limiting by 02 Absorption
12
Figure 1.4 Area covered by 2.4GHz and 60GHz frequency
13
Figure 1.5 Electro magnetic spectrum
16
Figure1 .6: Block diagram of Radio Frequency communication
17
Figure 1.7.: Fields confined in two directions only
20
Figure 1.8.-Fields confined in all directions.
20
Figure 1.9.- Waveguide shapes.
22
Figure 1.10. :Labeling waveguide dimensions.
23
24
Figure 1.11 : Simple electric fields . CAPACITOR.
Figure 1.12: E field of a voltage standing wave across a 1-wavelength section of
a waveguide
25
Fig . 1.13Direction of Electric Field of a waveguide(First Boundary condition) 26
Figure 1.14- Magnetic field in a wavegu ide three half-wavelengths long .
27
Fig.1.15 H field boundary condition
27
Fig .1.16 Waves traveling through a waveguide
28
Fig.1.17Pyramidal horn
30
Fig .1.18 Conical Horn
30
Fig.1.19 Dipole
31
Fig.1.20 Connection of dipole with waveguide of horn anten na
32
Figure.1.21 RLC series circuit
33
Figure1 .22 : Crystal oscillator
35
Fig.1.23 H-plane dimensions of a pyramidal horn antenna
39
Fig.1.24 How to separate the coaxial cable in a dipole
49
7
CHAPTER 1
INTRODUCTION
1.1 Introduction to Wireless Comm unication System
In today's technological society, wireless communication has become an
increasingly important part of daily life. We have come to depend on our pagers,
cellular phones, satellite dishes, radios, etc., usually without understanding how
they work. The common element to all of these wireless systems, whether they
transmit or receive, is the antenna. Wireless communications involves the
transfer of information between two points without direct communication. This
can be accomplished using sound, infrared, and optical or rad io frequency
energy but most modern wireless systems rely on RF or microwave signals.
Because of spectrum crowding , and the need for higher data rates, the trend is to
higher frequencies. Recently, frequency range of 60GHz is unlicen sed and if
implemented properly can put the communication level to a much higher level in
terms of speed and data transfer.
8
1.260 GHz Frequency System
1.2.1 Unlicensed bandwidth
There is a general trend in wireless communications to move towards higher
frequencies . Due to wider bandwidths, and ability to penetrate fog , dust, fol iage,
even buildings and vehicles to some extent make higher freq uencies more
suitable. [1]Now the recent researches are on 60 GHz as the re are several
r
benefits in this frequency.
A major factor in this allocation with commercial benefits is that the spectrum is
"unlicensed" - in other words, an operator does not have to buy a license from
the FCC before operating equipment in that spectrum.
The licensing process typically is very expensive and time consuming. Point-topoint wireless systems operating at 60 GHz have been used for many years by
the intelligence community for high security com munications and by the military
for satellite -to satellite communications.
Norih America
Europe
Aual,..lia
64
66
Unlicensed Spectrum (In Gfk)
Figure 1 International unlicensed spectrum around 60 GHz
Figure 1.1 Unlicensed spectrums
9
While contemporary unlicensed systems support light and moderate levels of
wireless data traffic, as seen in Bluetooth and wireless local area networks
(WLANs), current technology is unable to supply data rates comparable to
wired standards like gigabit Ethernet and high-defi nition multimedia interface
,...
(HOM I). Fortunately, as illustrated in Figure 1, an abund ance of widely available
spectrum surrounding the 60 GHz (60G) operating freq uency has the ability to
support these high-rate, unlicensed wireless
communications. [3]
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1.2.2 Reasons of using 60 GHz frequency
One of the special characteristics is the oxygen molecule (02) absorbs
electromagnetic energy at 60 GHz most (Figure 2). This absorption occurs to a
much higher degree at 60 GHz than at lower frequencies typically used for
wireless communications. This absorption weake ns (attenuates) 60 GHz signals
over distance, so that signals cannot travel far beyond their intended recipient.
For this reason , 60 GHz is an excellent choice for cove rt satellite-to-satellite
communications because the earth's atmosphere acts like a shield preventing
earth-based eavesdropping . However, this frequen cy ca n also be used in office
environment.[6]
,.
..
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f
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1':
•
•
>0
I
./
••
••
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i -FCC"_on
./
"' 0
••
04
1. .
1' 0
120
Figure 1.2 Attenuation versus frequency
10
,..
In addition to the high-data rates that can be accomplished in this spectrum ,
energy propagation in the 60 GHz band has unique characteristics that make
possible many other benefits such as excellent immunity to interference,
high security, and frequency re-use.
Another consequence of oxygen absorption is that radiation from one particular
60 GHz rad io link is quickly red uced to a level th at will not interfere with other 60
GHz links operating in the same geographic vicinity. This red uction enables
higher "frequency reuse" - the ability for more 60 GHz links to operate in the
same geographic area than links with longer ranges. As an example, two
different links can be compared, one operating near 60 GHz and the other at a
frequency that is less affected by 02 absorption. The second link could be
operating at another unlicensed frequency such as 2.4 GHz or 24 GHz. Consider
r
a typical operating scenario where both links are operating over a distance of one
kilometer with the transmitter's power output adjusted such that the signal level at
the receiver is 30 decibels (dB) above the background noise. Figure 3 shows
how the signal level drops with distance beyond the receiver in the two cases.
For the link unaffected by 02 absorption , it ta kes 32 kilometers (km) for the
transmitted signal to drop down to the background noise level. In other words,
that signal wou ld interfere with any other signal at that same frequency for more
than 30 kilometers beyond its original recipient. That red uces the number of links
at that frequency that can be installed in a fairly large area. Also, th is means that
the lower-freq uency signal cou ld be intercepted up to more than 30 kilometers
beyond its intended recipient. In contrast, the tra nsmitted signal at 60 GHz drops
down to the noise level in a mere 2.5 km . Consequently, more 60 GHz links can
be used in the same area without worrying about interference. Also, the 60 GHz
links are far more secure given their limited range .[6]
11
E ffec t o f 02 abs o rption o n
Cl e a r AI r sig nal p r op ag ati o n
80 ~-----------------------------------------,
40
aD
E
30d 6
~
0
.5!
Noise F loO!'
~
c
.2'
'"
-40
-8
o
r
1
10
1
0
Figure 1.3 Radiations Limiting by 02 Absorption
The combined effects of oxygen absorption and narrow beam spread res ult in
high security, high frequency re-use, and low interference for 60 GHz links.
Figure 4 shows two buildings th at are 1 km apart. The wedges show th e rad iation
pattern from 2.4, 24 and 60 GHz links operating with the same performance at 1
km . The links have equivalent 1-foot diameter antennas. The three wedges sh ow
the locations where the radiation at each frequency remain s high. The largest
wedge represents the radiation pattern from a 2.4 GHz link. The 60 GHz link has
the narrowest and shortest wedge and can be barely be seen except in the blowup. The wedges for 2.4 and 24 GHz links are substantially larger than the 60
GHz link, even though th eir operational link distance is the same (1 km).
12
Figure 1.4 Area covered by 2.4GHz and 60G Hz frequency
The practical implications of these graphics are obvious. A 60 GHz link can only
be intercepted in the tiny wedge and will only interfere with another 60 GHz link
in that wedge. A 24 GHz link has interference and interception risks over a much
longer and somewhat broader wedge, while a 2.4 GHz link has interference and
interception risks over a very large area, both in distance and in breadth.[6)
The 60 GHz band is an excellent choice for high-speed Internet, data, and voice
communications offering the following key benefits:
-Unlicensed operation - no need to spend significant time and money to obtain a
license from FCC
13
-Highly secure operation - resulting from short transmission distances due to
oxygen absorption and narrow antenna beam width
-Virtually interference-free operation -
resulting from
short transmission
distances due to oxygen absorption, narrow antenna beam width , and limited use
of 60 GHz spectrum
-High level of frequency re-use enabled - communication needs of multiple
customers with in a small geographic reg ion can be satisfied
-Mature technology - long history of this spectrum being used for secure
communications·16]
1.3 Electromagnetic energy
The definition of electromagnetic energy can be given as, the energy source
required to transmit information (in the form of waves) from one place (material)
to another. This information can be in the form of light, heat, or in any other form .
However, the very basic terms in order to know the exact meaning are discussed
below.
1.3.1 Electric Charge - It is an attribute of subatomic particles, that determines
their interactions when placed in electric and magnetic field. Electrically charged
matter
has
as
well
as
gets
affected
by
electromagnetic
field .
1.3.2 Electric Current - It is the movement or flow of electrica lly charged
particles. There are two types of charged particles namely, positively charged
particles
i.e.
protons
and
negatively
charged
particles
i.e.
electrons.
1.3.3.Magnetism - Magnetism is a force that affects the interaction of materials
or moving charged particles, by developing attractive or repu lsive forces between
them .
r
14
1.3.4 Electromagnetic Wave Energy - It is a wave created by the acceleration
of charged particles that are placed in magnetic and electric field ; both the fields
acting at right angles to each other. The oscillation of the particles in the wave
emits energy called as electromagnetic wave energy.
1.3.5 Electromagnetic Spectrum Energy - A ra nge of electromagnetic waves of
all possible frequencies and wavelengths forms an electromagnetic spectrum .
The total energy of the spectrum is called electromag netic spectrum energy.
1.3.6Electromagnetic Radiation Energy - Electromag netic radiation is a
collection of electromagnetic waves traveling in vacuum or in matter. The energy
radiated by the electromagnetic waves is called electromagnetic radiation
energy.
1.3.7Electromagnetic Field Energy - Electromagnetic field is caused by
electrically charged objects, that influences the behavior of materials or charged
particles around the field . The total amount of energy of the field and the
materials it affects is called electromagnetic field energy.
1.3.8 Electromagnetic Energy Facts
•
The different types of electromagnetic waves are light, microwaves , xrays , and TV and radio transmissions(4).
•
Here is a list of the electromagnetic waves in the decreasing order of their
frequencies that constitute the electromagnetic spectru m:
1. Gamma rays
2 . X-rays
3. Ultraviolet rays
4. Visible light rays
,..
5. Infrared rays
6. Microwaves
7. Radio waves (FM)
15
8. Radio waves (AM)
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9. Long radio waves
-
THE ELECTRO MAGNETIC SPECTRUM
Wavelength
(tl"IE:tft~$ )
Radio
M icrowave
Infrared
Visible
Ultravi olet
10-8
X-Ray
10- 10
Gamma Ray
10. 12
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Frequency
(Hz)
Figure 1.5 Electromagnetic spectrum
o
Higher the energy of the particles of electromagnetic wave, shorter is the
wavelength .
o
Electromagnetic waves travel th rough any material as well as thro ugh
vacuum.
o
The ve locity of electromagnetic waves in vacuum is same as that of light,
i.e. approximately 1,86 ,000 miles per second or 3,00,000 kilometers per
second.
o
When electromagnetic waves enter matter, they slow down I.e. their
energy decreases, hence wavelength increases.
o
r
When any object is heated , its particles are acce lerated that ca uses
change
in
their
electric
and
magnetic
fields,
thus
forming
an
electromagnetic wave. Whereas when an electromagnetic wave hits an
16
object, it generates heat at the surface that in tu rn causes the particles of
that object to vibrate. The heat and vib ration of the particles depends on
the wavelength and energy of the electromagnetic wave.
We utilize electromagnetic energy in our day-to-day life without being aware of its
existence.
1.4 Radio Frequency (RF) communication
Radio frequency (RF) radiation is a subset of electromagnetic rad iation with a
wavelength of 100 km to 1 mm, which is a frequency of 3 kHz to 300 GHz,
respectively. This range of electromagnetic radiation constitutes the radio
spectrum and corresponds to the frequency of alternating current electrical
signals used to produce and detect radio waves. RF can refer to electromag netic
oscillations in either electrical circuits or radiation th roug h air and space. Like
other subsets of electromagnetic radiation , RF travels at the speed of light.
Antenna
Microphone
Amplifier
ModUdltor
Transmitter
Antenna
Loud
Amplifier
Demodualtor
~
AudiO
am plifter
~r
Receiver
Figure1.6: Block diagram of Radio Frequency communication
17
1.4.1 Microwave frequency
Our thesis deals with the microwave range of frequency.
Microwaves are electromagnetic waves with wavelengths ranging from as long
as one meter to as short as one millimeter, or equivalently, with frequencies
between 300 MHz (0.3 GHz) and 300 GHz.
This range is situated between radio waves and infrared radiation. They are the
principal carriers of television, telephone, and data tra nsmissions between
stations on Earth and between the Earth and satellites.
Microwave frequency bands, as defined by the Radio Society of Great Britain
(RSGB) , are shown in the table below:
Table: Microwave freque ncy bands
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Letter Designation
Frequency range
L band
1 to 2 GHz
S band
2 to 4 GHz
C band
4 to 8 GHz
X band
8 to 12 GHz
Ku band
12 to 18 GHz
K band
18 to 26. 5 GHz
Ka band
26.5 to 40 GHz
Q band
30 to 50 GHz
U band
40 to 60 GHz
V band
50 to 75 GHz
E band
60 to 90 GHz
Wband
75 to 110 GHz
F band
90 to 140 GHz
D band
110 to 170 GHz
18
Microwave freq uencies present special problems in tran smission , generation ,
and circuit design that are not encounte red at lower frequencies. Conventional
circuit theo ry is based on voltages and currents while microwave theo ry is based
on electromagnetic fields.
Now the accord ing to the range of frequency, there are different frequency bands
as shown in the chart above. [2]
1.5 Transferring of electromagnetic waves
1.5.1 The two-wire transmission line: used in conventional circu its is inefficient
for transferring electromagnetic energy at microwave frequencies. At these
frequencies , energy escapes by radiation because the field s are not confined in
all directions (Fig-1.7)
FIEL DS NOT CONFINED
IN TH IS DIRECT IO N
!;ND VlEW O F TV\,O WlRE LI NE
Figure 1.7.:Fields confined in two directions only
19
1.5.2Coaxial
lines:
More
efficient
than
two-wire
lines
for
transferring
electromagnetic energ y because the fields are com pletely confined by the
conductors, as illustrated in fig ure 1-2
F l\!n V IFW O F COAXIA l \:AR I F
Figure 1.8.-Fields confined in all directions.
1.5.3 Waveguides are the most efficient way to transfer electromagnetic energy.
WAVEGUIDES are essentially coaxial lines without center conductors
A hollow conductive metal pipe used to carry high frequ ency radio waves,
particu larly microwaves. In other words, it is used to gu ide electromagnetic
waves at microwave frequency regions. They are constructed from conductive
material and may be rectangular, circu lar, or elliptical in shape, as shown in
figure 1-3.
20
,..
ELLIPTICAL
CIRCULAR
RECTANGLE
Figure 1.9.-Waveguide s hapes.
1.5.3.1Waveguide Advantages
Waveguides have several advantages over two-wire and coaxial transmission
lines. For example, the large surface area of waveg uides greatly reduces
COPPER (1 2R) LOSSES. Two-wire transmission lines have large copper losses
because they have a relatively small surface area. The surface area of the outer
conductor of a coaxial cable is large, but the surface area of the inner conductor
is relatively small. At microwave frequencies , the current-carrying area of the
inner conductor is restricted to a very small layer at the surface of the conductor
by an action called SKIN EFFECT.[7]
Power-handling capability is another advantage of waveguides. Waveg uides can
handle more power than coaxial lines of the same size because power-handling
capability is directly related to the distance between conductors [5].
However, wavegu ides have certain disadvantages that make them practical for
use only at microwave frequencies.
21
1.5.3.2Waveguide Disadvantages
Physical size is the primary lower-frequency limitation of waveguides. The width
of a wavegu ide must be approxi mately a half wave length at the frequency of the
wave to be transported . For example, a wavegu ide for use at 1 megahertz would
be about 500 feet wid e. This makes the use of waveguides at frequencies below
1000 megahertz increasingly impractical. The lower freq uency range of any
system using waveguides is limited by the physical dimensions of the
waveguides . Waveguides are difficult to install because of their rigid , hollow-pipe
shape. Special couplings at the joints are req uired to assure proper operation.
Also, the inside surfaces of waveguides are often plated with silver or gold to
redu ce skin effect losses. These requi rements increase the costs and decrease
the practicality of waveguide systems at any other than microwave frequencies.
1.6 Waveguide design
1.6.1 Dimensions
As shown in figure 1-9, the widest dimension of a waveguide is called the "a"
dimension and determines the range of operating frequencies. The narrowest
dimension determines the power-handling capability of the waveguide and is
called the "b" dimension.
r----: --t
IO
"
11[,
.L ....._ .....
I
WAVEGUIDE 1
WAVEGUIDE 2
Figure 1.10.:Labeling waveguide dimensions.
22
In practical applications, the wide dimension of a waveguide is usually 0.7
wavelength at the operating frequency. This allows the waveguide to handle a
small range of frequencies both above and below the operating frequency. The
"b" dimension is governed by the breakdown potential of the dielectric, which is
usually air. Dimensions ranging from 0.2 to 0.5 wavelength are common for the
"b" sides of a waveguide.[7)
In our making of antenna we used the standard USA and European Waveguide
sizes with their Pertinent Mechanical and Electrical Parameters[8) which is
attached at the end of the report.
Since energy is transferred through waveguides by electromagnetic fields , it is
important to have a basic understanding of field theory. Both magnetic (H FIELD)
and electric field (E FIELD) are present in waveguides, and the interaction of
these fields causes energy to travel through the waveg uide. This action is best
understood by first looking at the properties of the two individual fields . E
FIELD.-An electric field exists when a difference of potential causes a stress in
the dielectric between two points. The simplest electric field is one that forms
between the plates of a capacitor when one plate is made positive compared to
the other, as shown in figure 1-11A. The stress created in the dielectric is an
electric field . Electric fields are represented by arrows th at point from the positive
toward the negative potential. The number of arrows shows the relative strength
of the field . In figure 1-1 1A, for example, evenly spaced arrows indicate the field
is evenly distributed. For ease of explanation, the electric field is abbreviated E
field , and the lines of stress are called E lines.
23
+
+
"='
I
Figure 1.11: Simple electric fiel ds. CAPAC ITOR.
Figure 1.1 2, view (A), shows the E-field pattern created by a voltage sine wave
applied to a one-wavelength section of waveguide shorted at one end . The
electric fields are represented by the arrows shown in views (8) and (C). In the
top view of view (A) , the tip of each arrow is rep resented by a dot and the tail of
each arrow is represented by an X. The E field varies in density at the same sinewave rate as the applied voltage. This illustration represents the instant that the
applied voltage wave is at its peak. At other times, the voltage and the E field in
the waveguide vary continuously from zero to the peak value. Voltage and E-field
polarity reverse with every reversal of the input. Note th at the end view shown in
view (8) shows the E field is maximum at the center and min imum near the walls
of the waveg uide. View (C) shows the arrangement of electromagnetic fields
within a three-dimensional waveguide.
24
VO LTAGE STA NDIN G 'NAVE
-
f
I
,
./
"o"DIN .
- _ /
'
~1
,••
.J...
~
(Bl END VI [W
2~
- 4-
...'.
F
--I
.
!.-
. ~
•
- ... :,"
---1lc L..'_'_'_:;_r_:_._
. _'_.._~_:_;~_;:_'_:_'-I
TOP VIE'"
~ SHORTEO
~E ~l
ll llmll"TT"O"TTll
llllTlTl '1'T T " iml l ,~
SI DE VIEW
(A) tE NGHT"'ISE \/IE'"
Ie) THREE OIY ENSIO NAL \/ IE'"
Figure 1,12:.E field of a voltage standing wave across a 1-wavelength
section of a waveg uide
Two conditions , known as BOUNDARY CON DITIONS, must be satisfied for
energy to travel through a waveguide.
E FIELD
Fig. 1.13Direction of Electric Field of a w aveguide(First Boundary
condition)
25
In order for the energy to travel through waveg uide and for the electric field to
exist at the surface of a conductor it must be perpendicular to the conductor as
shown in the above diagram.
H FIELD.- The magnetic field in a waveguide is made up of magnetic lines of
force that are caused by curre nt flow through the conductive material of the
waveguide. Magnetic lines of force, called H lines, are continuous closed loops.
All of the H lines associated with current are collectively called a magnetic field or
H field. The strength of the H field , indicated by the number of H lines in a given
area , varies directly with the amount of current.
No H lines ca n form outside the wavegu ide as long as it is completely enclosed .
Figure 1-13 shows a cross-sectional view of the magnetic field pattern .It must be
noted in view (A) that the field is strongest at the edges of the waveguide where
the current is highest. The minimum field strength occurs at the zero-current
points. View (8) shows the field pattern as it appears 1/4 from the end view of the
waveguide.
.
..•.•
.. ,. 1
•. •..•
..
••
"
"
~ Tn O HG
II rin D
(A)
TOP VIEW
(9)
END VIEW
Figure 1.14-Magnetic field in a waveguide three half-wavelengths long .
26
to! F IF I
n
E IEL ·
Fig.1.15_H field boundary condition.
The second boundary condition states that, for a varying magnetic field to exist,
it must form closed loops in parallel with the conductors and be perpendicular to
the electric field.Since an E field causes a current flow that in turn produces an H
field , both fields always exist at the same time in a waveguide. If a system
satisfies one of these boundary conditions, it must also satisfy the other since
neither field can exist alone.
Electromagnetic energy transmitted into space consists of electric and magnetic
fields that are at right angles (90 degrees) to each other and at rig ht angles to the
direction of propagation(7).
Fig.1.16 Waves traveling through a waveguide
27
1.7 Horn antenna
Horn antennas are very popular at UHF (300 MHz-3 GHz) and higher
frequencies .They often have a directional rad iation pattern with a high gain ,
wh ich can range up to 25 dB in some cases, with 10-20 dB being typical. Horns
have a wide impedance bandwidth , implying th at the input impedance is slowly
varying over a wide frequency range (which also implies low va lues for S11 or
VSWR). The bandwidth for practical horn antennas ca n be on the order of 20:1
(for instance, operating from 1 GHz-20 GHz) , with a 10:1 bandwidth not being
uncommon.
The gain often increases (and the beamwidth decreases) as the frequen cy of
operation is increased. Horns have very little loss, so the directivity of a horn is
roughly equal to its gain.
Horn antennas are somewhat intuitive and not relatively simple to manufacture.
In addition, acoustic horns also used in transmitting sound waves (for example,
with a megaphone) . Horn antennas are also often used to feed a dish antenna,
or as a "standard gain" antenna in measurements.
1.7.1 Why Horn Antenna
As we are dealing with a very high freq uency of 60 GHz, a horn antenna is more
suitable over other antennas for this project, as wired antennas are used at very
low frequency.
However the main advantage of the horn antenna is th at it provides a significant
level of directivity and gain. For greater levels of gain the horn antenna should
have a large aperture. Also to achieve the maximum gain for a given aperture
size, the taper should be long so that the phase of the wave-front is as nearly
constant as possible across the aperture.
Another reason to choose horn antenna is- it is easy to build as fabrication not
needed unlike microstrip patch antenna. A microstrip patch antenna is a
28
narrowband , wide-beam antenna fabricated by etching the antenna element
pattern in metal trace bonded to an insulating dielectric substrate with a
continuous metal layer bonded to the opposite side of the substrate which fo rms
a groundplane. This process is expensive and time consuming.(8)
1.7.2 Classification of horn antenna
1.7.1 Pyramidal horn
LE
E
Fig.1.17 Pyramidal horn
1.7.2 Conical horn
Fig.1.18 Conical Horn
29
1.8 Dipole
A dipole is a very basic antenna structure consisting of two straight collinear
wires as depicted in Figure 1. The first thing to notice about a dipole is that it has
two parts, hence the term "di" in its name.
Fig.1.19 Dipole
It is wid ely used on its own, and it is also incorporated into many other RF
antenna designs where it forms the radiating or driven element for the
antenna.
Ad ipole is an antenna that is a resonant 1/2 wave in length . It has 2 electric
poles (at the ends) of opposite polarity at any given instance. A dipole can be
fed with RF energy anywhere along its length although center feed is the
most common followed by end feed[9].
30
Fig.1.20 Connection of dipole with waveguide of horn antenna
The open ended waveguide attached with the horn antenna must be added with
the dipole. The wavegu ide end must be closed with a metal part so the waves
generating from the dipole can reflect from the closed end . The above diagram
shows the connection of dipole with waveguide of horn anten na.
1.9 Oscillator
In order to make 60GHz voltage source generator it is important to know the
operations of simple oscillator and Crystal oscillator.
1.9 Oscillator
Oscillators are active devices that generate power at a frequency determined by
circuit parameters . The circuit forms a harmonic oscillator for cu rrent and will
resonate
31
An important property of RLC circuit is its ability to resonate at a specific
frequency, Resonance occurs because energy is stored in two different ways: in
an electric field as the capacitor is charged and in a magnetic field as current
flows through the inductor. Energy can be transferred from one to the other within
the circuit and this can be oscillatory. The reson ance frequency in a series or
parallel resonant circuit has the value[10]
wo=
1
JLC
I
---7
R
v
+
L
c
Figure.1.21 RLC series circu it
v - the voltage of the power source
I - the current in the ci rcuit
R - the resistance of the resistor
L - the inductance of the inductor
C - the capacitance of the capacitor
32
1.9.1 Crystal Oscillator
A crystal is a solid material that vibrates at a specific frequency when energy is
supplied .
When a crystal of quartz is properly cut and mounted , it can be made to distort in
an electric field by applying a voltage to an electrode near or on the crysta l. This
property is known as piezoelectricity. When the fi, ld is removed , the quartz will
generate an electric field as it returns to its P, ViOUS shape, and this can
generate a voltage. The result is that a quartz crystal behaves like a circuit
composed of an inductor, capacitor and resistor, with a precise resonant
frequency.
Quartz has the further advantage that its elastic constants and its size change in
such a way that the frequency dependence on temperature can be very low. The
specific characteristics will depend on the mode of vibration and the angle at
which the quartz is cut (relative to its crystallographic axes) Therefore, the
resonant frequency of the plate, which depends on its size, will not change much,
either. This means that a quartz clock, fi lter or oscillator will rema in accurate.
A quartz crystal can be modeled as an electrical network with a low impedance
(series) and a high impedance (parallel) resonance point spaced closely together
33
<>-----i 0 1----0
Co
Figure1.22 : Crystal oscillator
where s is the complex frequency (s = jw).
Ws
is the series resonant frequency in
radians per second and wp is the parallel resonant freq uency in radians per
second .
However. for this project crystal is required but unfortunately it is not available in
our country. It is not possible to build a source without the crystal for such a
high frequency range of 60GHz.
34
Chapter 2
Design and Cal culations
2.1 Waveguide
WAVEGUIDE SIZ E CHART
USA
WR{s;u)
Europe
WG.
(size)
START
Frequency,
(GIrL)
STOP
Frequency
(GIrL)
32
35
.41
.4\\J
0.64
.750
960
1.120
1.45
1.70
220
2.60
3.30
3.95
4.90
5.85
7.05
7.00
8.20
10.00
12.40
15.00
18.00
2200
2650
33.00
4)00
5000
6000
75.00
90.00
110.00
140.00
.49
53
.62
.750
096
112
1.46
1.70
2.20
2.60
lJO
3.95
4.90
5.85
7.05
8.20
10.00
11.00
12.40
15.00
18.00
22.00
26.50
33.00
40.00
50.00
60.00
75.00
90.00
110.00
141.00
17000
220.00
TEI0
TE20
WTOFF
Frequency,
WTOFF
Frequency,
(GHz.)
O.ll
0.56
0.65
0.78
1.02
121
U3
1.82
231
2.74
147
4.15
5.15
63
7.42
8.60
10.l1
ILl7
13.11
15.73
1897
23.14
28.1
34.71
(GH~)
2300
2100
1800
1500
1150
975
770
650
510
430
340
284
229
187
159
137
112
102
90
75
62
51
42
34
28
21
19
15
12
10
8
7
5
6
8
9A
10
IIA
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
Tl
28
29
30
0.256
018
032
0.39
051
0.60
0.76
o.m
1157
IJ72
1.736
2.078
2577
3.152
3.711
4JOI
5259
5.785
6557
7.868
9.486
IU74
14.047
17328
21D!
2634
3136
39.86
4835
59Dl
73.60
90.90
115.7
4W
52.69
62.78
79.74
96.74
118.0
147Jl
18Ll
231.42
Inside
Dimension
".'
23.1XXl
21.1XXl
18.1XXl
15.1XXl
ILloo
9.750
7.700
6.l00
5.100
4300
3.4))
2.841
2.2W
1.872
U90
IJ72
1122
1.020
.900
.750
.622
.lID
.420
.l4O
.280
.224
.188
.148
.l22
.100
.0800
.0650
.0510
Inside
Dimension
Inside Tol:
(±)
Wall
Thickness
(Ill)
1I .lOO
1O.lOO
9roJ
7.lOO
5750
4.875
U50
3250
2550
2.150
1.700
1341
1.145
0.872
0.795
0.622
0.497
0510
.400
375
311
.255
.170
.170
.140
.ll2
.094
.074
.061
.050
002
.02
.15
.125
.125
',.
.00)
.0325
0255
om
.015
.015
.010
DIO
.010
.010
.008
.005
.005
.005
.005
.004
.004
.004
.003
.003
.003
.002
.002
.002
.DOl
.002
.001
.001
.001
.0005
roJ5
DOO3
.OD02
0002
35
om
125
125
.125
.080
.080
.080
.080
.080
.M4
D64
.M4
.M4
.M4
.064
.050
.050
.04)
.04)
.04)
.04)
.04)
.04)
.04)
.041
.04)
.04)
.020
.020
.020
From the above chart[8], the frequency range of 10GHz to 15GHz is chosen to
calculate the horn antenna design parameters. This frequency range has a size
of WR-7 5(USA) and WG-17(Europe). The waveg uide dimensions found from this
range are wider dimension 'a' of 0.75 inches and narrowe r dimension 'b' of 0.375
inches.
In general, 'a' dimension as suggested in the previous chapter must be 0.7 of the
wavelength and 'b' dimension between 0.2 to 0.5 wavelength.
Now calculating whether the value obtained from the chart matches the criteria
mentioned above.
Calcul at ing waveg uide dimens ions
For 10 GHz
+
9 - 1
f := 10·10 s
c
).. := -
f
).. = O.03 m
a := 0.7 ·)..
a = 0 .021 m
bl := 0.2 · )..
bl
= 5.996
x 10- 3 m
b2:= 0 .5 · )..
b2 =0 .015m
b := .o...(b_l_+_b_2)
..<..
2
b = 001 m
36
Comparison between standard a nd
calculated values
• 10 GHz
Standard Values
(cm)
Cal culated valu es
(cm)
% differen ce
a
1.905
2.1
0.102
b
0.952
1
0.05
As it is seen from the above ta ble, the percentage difference came to be less so
our ca lculated values came to be correct.
37
2.2 Horn antenna
In order for accurate design of an optimum gain horn antenna all the design
parameters and formulas are taken from an electronic letter(1 2).
Fig.1.23 H-plane dimensions of a pyra midal horn antenna
'til ""
[Jq3 +1'2
,r/8 - [Jq3
q=
2
99(49 -
r2 -
rf1a
Clb)
G).2
9 - -6.464
38
2 g2 _ '«
_
_\
3
{,. ::; 0.1
n
2
!.4 + (!!l)2
3,\
39
r
2.2.1 60 GHz horn antenna calculations
Different antenna parameters for 10 GH z frequencY
For frequency range 60 - 90 GHz waveguide di mensions are :
al := .122 em
bl := ,061 em
where waveguide si ze is WG·17 (Europe) and WR·75(USA)
considering a gain of 20 dB
01 := lOa
Our purpo se is to deal with 60GHz range so taking th e above dimensions to calculate
different parameters,
fre queney
9 -I
fi := 60, 10 s
8
speed of light e = 2998 x 10 ~
s
wavelength
e
A:= -
fi
A= 4997 x 10-3 m
Al := .5
em
Now we need to calculate the dimensions of the antenna and fo r that we need to
calculate few parameters which are found out below,
40
2
Gj.).,1
gl := - 6.464
gl
3.868
=
em
2[(2'3 al 2) - bl2lJ
r := '3I (gl) ·
r = 0.031
em
2
q := - gl ·(4·gl- albl)
9
q =13.29
-- --
+
-
-
- ----...
3
-
-
3r.--===---:q3 + + r - ~ q3 +
r'
ul := ~
ul
em
J l
J l-
1.551 x em' 3
=
WI.]
l4 )
-bl
21 := [ -2- + ~
+ ul
21 = 0.019
41
Bl
Bl - 1 .7 77
em
Al :- ~
Bl
Al
L e :-
= 2 .177
e rn
BIJ + (~:)2
+
2
L. = 3 .28
L1 - 3 .157
e rn
e rn
3·),,1
Lh - 3 .341
ern
L2 - 3. 159
em
P . :_ Ll . ( B I - bl)
BI
Ph := L2 . (A I - .. I)
Al
Ph - 2 .982
( AI )2
P . - 3 .049
em
em
Now, ca lcu lating the gain us ing th is above values
BI
02 := 6 .464·A I · 2
>-'1
02 = 100
So , th e above diameters are c orrect t o b uild th e ho rn ant enna of 20 dB g ain .
42
2.2.2 10GHz horn antenna calculations
Different :lOte"na parameters tor 10 GH z frequency
For frequency range 10 - 15 GHz wavegui de dimensi ons are :
a = .750
inches
b =, .375
inche s
Conve rting into cm we get
al := 1.9
bl := .95
cm
cm
where wavegui de size is WG- 17(Europe) an d W R-75 (U SA)
con sidering a ga in of 20 dB
Gi := 100
Our purpo se is to deal with 10GHz ra nge so ta king the above dim ensio ns to calculate
different parameters .
frequency
9 - I
Ii := 10·10 s
spee d of li ght
wavelength
8
c = 2.998 x 10 ~
s
>...=
c
-
Ii
A= 0.03m
AI :=3
cm
43
Now we need to calculate the dimensions of the ant enna and for that we need to
calculate few parameters which are found out below.
Qj.}..1
2
gl : = - 6.464
gl
=
r :=
139.233 em
~(gll[GaI2) - b1 2]
3
r = 9.72 x 10 em
2
q := -gl (4g1- al ·bl)
Q
q = 1.718 x 10
ul
=
0.377
4
em
em
44
21
.~ [-~1
21
Bl
.~
.
+ Ul]
0 .301
~
J21 2 + 4 ·22
2
Bl
Al . ~
J[b~2J
+
em
10 .654
~
gl
Bl
-
Al
~
em
13 .068
Lh . ~
em
L e - 19 .655
L1
~
18.92
em
AI
~
16.216
Lh
~
20 .068
em
L2
~
18 .9 75
em
Pe :~ Lt. ( BI - b l)
BI
Ph .~ U . (A I - al)
Ph
AI·
Pe
em
~
17 .233
em
Now, calc ulating t he gain us ing thi s above valu es :
Bl
G2 := 6 .464Al · -
+
>-'1
G2
~
2
100
So , the . above diam eters are correct t o build t he horn anten na of 20 dB gain.
45
2.3 Dipole design
First it is important to find
some coaxial AWG wire. The thicker the wire the
greater the operating bandwidth of the antenna. Often 12 AWG is used.
Next step is to cut the wire for the frequency at which it wi ll operate. The formula
shown below is used to calcu late the dipole length, which is more accurate.
Length (feet) = 468 1 Frequency (MHz)
or
Length (meters) = 1441 Frequency (MHz)
However, the dipole length is usually half of the wavelength calcu lated from the
equation below. But the length of the dipole calcu lated this way gives comes
much longer.
wavelength
c
). .= -
Ii
46
Dipole calculations
• Two formulas
Formula 2 :
Fonnula 1:
Length (meters) 1441
Frequency (MHz)
=
Freque ncy(GHz)
Dipole len gth=wavelength / 2
Wa -.elength (
mm)
Fonnaula
1(mm )
2(mm)
10
30
14
15
60
5
2.4
2.5
Fonnaula
A wavelength (or fraction of) in coax cable is physically shorter than calculated
from the form ula for wavelength . As the formu la used to calculate the wave length
was probably meant for calcu lating a "free space" (air) wavelength . In fact, RF
energy moves more slowly in a transmission line than it does in air because the
materials used in cable slow it down . Therefore, a wavelength in cable takes up
less length.
Its important to add enough extra length to these dimensions ca lculated from the
dipole formula for wrapping
around the insulators. Its important to have two
equal lengths of wire.
Insulators should support th e weight of the wire, withstand ultraviolet radiation
from the sun , and not absorb moisture. The center insulator will only have a small
voltage across it
There should be a wire attached to each end of the center insu lator and one
insulator to the end of each free wire.
47
This version of the dipole will be fed with coax cable. Now the coaxial cable is
separated as shown in the diagram .
SEPARAn
PLlLL
rlIC___- C; Ii NTE R
CONOLAC.T
OUT
Fig.1.24 How to separate the coax ial ca ble in a dipole
48
Calculation of dipole length:
For GO Ghz frequency dipole le ngth
Ll:=
+
144
60000
-3
Ll = 2.4 x to
m
For 10 Ghz frequency
12 :=
144
10000
L2 = 0.014
III
For 100 MHz frequency di po le length
•
144
L., := 100
L3 = 1.44
III
49
Chapter 3
3.1 Conclusions:
We calculated the parameters for different kinds of antenna and made a 10 GHZ
transmittings antenna so that we can test this antenna with the receiving antenna
which is available in the lab. But due to absence of source for 10GHZ as the
source available in the lab had the output port is incorporated in to the antenna
system so we could not test it. But when the source will be available we can
make a 60GHz source and can test polarization diversity for 60 GHz.
As 60GHZ is a relatively new concept and we are the first group to research on it
we had could not make more progress as it consumed a lot of time finding the
design parameters for this frequency. Even the materials needed for testing a 60
GHZ antenna are not readily available in this country yet.
Further work:
We need 3-4 more weeks to get a voltage source and crystal oscillator to test 10
GHz antenna and to make 60 GHz voltage source in order that we can test
different kinds of polarization diversity.
50
References
[1] http://www.mindstien.net
[2] http://www.tpub .com/contenUneets/14182/css/14182_ 111 .htm
[3] 60 GHz Wireless Communications: Emerg ing Req uirements and
Design Recommendations Robert C. Daniels and Robert W . Heath , Jr.
The University of Texas at Austin
[4] http://www.khargoosh.ir/fa/images/electromagnetic-spectrum .jpg
[5]http://www.tudelft.nl/live/pagina.jsp?id=e2571 5a 1-4ge 1-43a3-ge858576cge2493f&lang=en
[6] Chris Koh, "The Benefits of 60 GHz Unlicensed Wi reless
Communications''http://wireless.fcc.gov/outreach/2004broadbandforum/comment
sIYDI_benefits60GHz.pdf
[7] http://www.tpub .com/contenUneets/14183/css/141 83_14.htm
[8] http://www.engineeringspecialties.neUwaveguide.htm
[9] http://www.hottconsultants.com/pdUiles/d ipoles-1 .pdf
[10] http://en .wikipedia.org/wiki/RLC_ci rcuit
[11 ] http://en.wikipedia.org/wiki/Crysta l_osciliator
[12] Selvan K. T. , "Accurate design method for optimum gain pyramidal horns"
IEEE Electronic Letter 18th Feb 1999
51